Chapter 10 - Genetics

What is Genetics?The study of heredity

Heredity: passing of traits from parent to offspring

Study of GeneticsChildren inherit traitsNeed to study many

generations

Review: GenesSection of DNA on

chromosomesPaired

1 from mom & 1 from dad

Gregor Mendel (1857)“Father of

Genetics”Discovered patterns

of inheritance by breeding pea plants

Mendel’s ExperimentsWhy pea plants?Easy to grow &

can be self pollinated Hypothesized that

“factors” carry information about traits

Flower Anatomy

Mendel’s Laws

Independent Assortment: traits are not inherited together

Segregation: Alleles separate when gametes are formed

What We Know Now“Factors” are called genesDifferent forms of a gene

are called allelesRepresented by letters

Ex. flower color alleles P (purple) or p (white)

AllelesCapital letter = dominant

allele Ex. P (purple)

Lower case = recessive allele

Ex. p (white)

Important VocabularyGenotype = alleles (letters)

that make up that traitEx. PP

Phenotype = physical appearance of trait

Ex. Purple

Homozygous: two of the same alleles (a.k.a. purebreed)

Ex. PP or ppHeterozygous: two different

alleles (a.k.a. hybrid)Ex. Pp

Important Vocabulary (Cont.)

Inheritance Of TraitsIf you inherit one dominant

allele the recessive allele will not be expressed

Predicting Our TraitsPunnett squares show

possible genotypes

Setting up a Punnett Square

g

g

G = Green g = White

Alleles from Mother

Alleles from Father

Interpreting Punnett Squares

G G

g

g

Gg Gg

GgGg

Offspring

Interpreting Punnett Squares (Cont.)

Offspring are:100 % HeterozygousTheir genotype is GgTheir phenotype is green

Monohybrid Cross:

Punnett Squares that analyze only one trait:

Depending on the parents alleles they can produce 1 or 2 different gametes for that trait.

Dihybrid Cross:

Punnett Squares that analyze two traits:

If both parents are homozygous for the two traits only one gamete can be formed (all heterozygous).

Dihybrid Continued:

If parents are heterozygous for the two traits than 4 types of alleles from male gametes and 4 types of alleles from female gametes can be formed.

Phenotypic Ratio is:

9:3:3:1

Genotypes: almost all different!

ProbabilityMeasure of how likely

something will occurEx. What is the probability

of getting heads when you flip a coin?

Ans. 50%

Punnett squares used to predict the probability of inheriting a trait!

Actual data not perfect- larger # of offspring more likely match the results predicted.

Probability

Recessive Genetic Disorders

Need to inherit two copies of recessive allele

Tay SachsSickle Cell

Anemia

More Recessive Genetic Disorders

Cystic FibrosisAlbinismGalactosemia

Dominant Genetic Disorders

Only need 1 copy of dominant allele

Polydactyly,

Marfan Syndrome

More Dominant Genetic Disorders

Huntington’s DiseaseAchondroplasia

Ch 11.2Complex Patterns of

Inheritance

Most traits are not simply dominant or recessive

Incomplete DominanceDominant & recessive

traits appear to "blend"

Ex. snapdragon flowers

red x white = pink

RR rr Rr

Incomplete Dominance A homozygous

dominant black cat is crossed with a gray cat and black is incompletely dominant over white. What is the percentage of having a gray kitten?

B B

b

B BB

Bb

BB

Bb

A gray cat is crossed with another gray cat and black is incompletely dominant over white. Complete a Punnett square and tell me what is the genotypic and phenotypic ratio of that cross?

Incomplete Dominance

Phenotypic ratio:

Genotypic ratio:

CodominanceTwo traits are

both fully seen

“Co”= together

Ex. Roan Horses have both red & white hairs

Codominance Both alleles should

be Capital letters since one is not dominant over another.

Cross: Roan Horse X Red Horse

R W

R

R

RR RW

RR RW

Codominance In humans, wavy hair (CS) results by

the co-dominance pattern of curly hair (C) and straight hair (S). What are the possible results if a wavy-haired man and a straight-haired woman have children?

List Genotypic and Phenotypic Ratios!

Multiple Alleles Two or more alleles

control the phenotype Ex. Human ABO blood

groups

Multiple Alleles A woman with type B

(heterozygous) blood and a man with type AB blood are expecting a child. What are the possible blood types of the kids?

A test was done to determine the biological father of a child. The child’s blood Type is B and the mother’s is Type A. Dude #1 has blood type O and dude # 2 has blood type AB. Which dude is the biological father?

Multiple Alleles

Polygenic Traits Traits that are controlled

by multiple genes Ex. height,

weight, hair color, skin color

Skin Color At least 7 different

Genes make up skin color!

Eye Color

Sex-Linked TraitsCarried on sex

chromosomes (X and Y)Most are recessive & on X

chromosomeColor blindness, hemophilia

Affect men more than womenMen have only one X chromosome

Women can be carriers or affected

Sex-Linked Traits (cont.)

Sex Chromosomes for Female are:

X XSex Chromosomes for male

are:

X Y

Sex-Linked Traits (cont.)

Fruit fly eye Color

R = Red eyes

r or w = white eyes

What is the probability of having a white eyed male?

Sex-Linked Traits (cont.)

A female fruit fly that is homozygous for red eyes mates with a male who has white eyes. What is the probability of having a female with white eyes?

Sex-Linked Traits (cont.)

A woman who is heterozygous for colorblindness has a son with a man who is colorblind. What is the probability that their son will be colorblind?

Sex-Linked Traits (cont.)

Polyploidy One or more extra chromosomes. 2n = normal number of

chromosomes Humans 46 chromosomes/ 23

pairs 1n = half the number of

chromosomes Sperm or Egg 23 chromosomes

Triploid (3n)– 3 complete sets of chromosomes.46 + 23 = 69

Most plants; sometimes earthworms and goldfish; Humans always Lethal!

Polyploidy

Karyotype: photographic arrangement of a complete set of chromosomes

Studying Inheritance

http://trc.ucdavis.edu/biosci10v/bis10v/media/ch08/karyotype.swf

FROM THIS……..

……TO THIS

Chromosomes # 1-22 are autosomes (body chromosomes)

Chromosomes # 23 are the sex chromosomes.

Looking at a karyotype you can see a chromosome mutation.

Studying Inheritance

______Chromosomal________Abnormalities

• 1 infant in 200 newborns has a chromosomal abnormality

• 28% of first trimester miscarriages have a chromosomal abnormality

• Abnormalities in larger chromosomes don’t usually survive

____________________________:Change in the ______________ or ____________ of chromosomes

CHROMOSOMAL MUTATIONS

structurenumber

Homologous chromosomes ________________ during MEIOSIS

= _________________________

One cell gets 2 copies of the chromosome the other cell gets none.

NONDISJUNCTION

fail to separate

Nondisjunction

Nondisjunction can lead to:

Down SyndromeTurner’s SyndromeKlinefelter’s Syndrome

Down syndrome (=____________)TRISOMY 21

Down syndrome (Trisomy 21)

1 in 800 births

Similar facial features

Slanted eyes

Protruding tongue

Turner syndrome

Turner syndrome ____

1 in 5000 births Females have only one X chromosome Small size Slightly decreased intelligence 35% have heart abnormalities Hearing loss common Broad chest Reproductive organs don’t develop at puberty Can’t have children

http://medgen.genetics.utah.edu/photographs/diseases/high/611.gif

XO

Klinefelter syndrome XXY

Klinefelter syndrome

1 in 1000 births Males have extra X chromosomes

(Can be XXy, XXXy, or XXXXy) Average to slight decrease in

intelligence Small testes/can’t have children Usually not discovered until puberty

when don’t mature like peers

Obtaining Fetal Cells ~Making a Karyotype~

1.Amniocentesis: sample of fluid around baby

2.Chorionic Villus Sampling: sample of tissue from the placenta

Amniocentesis

Chorionic Villus Sampling

Pedigree: chart that tracks the inheritance of a trait through multiple generations

Studying Inheritance (cont.)

Generation Symbols

P = Parental F1 = Offspring of P generation

F2 = Offspring of F1 generation

P Generation

F1 Generation

F2 Generation

Generation Symbols (cont.)

Interpreting the Pedigree

Carrier

Affected

Male

Female

Dominant Disorder Example:

Recessive Pedigree Example:

Create A Pedigree: One couple has a son and a daughter

with normal pigmentation. Another couple has one son and two daughters with normal pigmentation. The daughter from the first couple has three children with the son of the second couple. Their son and one daughter have albinism; their other daughter has normal pigmentation.